Agreement between Maternal Cannabis Use during Pregnancy according to Self-Report and Urinalysis in a Population-Based Cohort: The Generation R Study

Aim: To verify self-reported information on prenatal drug use in urine because reporting in pregnancy is sensitive to stigma and might lead to misclassification. Methods: Using semiquantitative immunochemical analysis, the presence of the urinary metabolite (11-nor-Delta 9-tetrahydrocannabinol-9-carboxylic acid) was compared to self-reported prenatal cannabis use. Sensitivity and specificity for self-report and urinalysis outcomes were calculated and Yule's Y was used as an agreement measure. Results: Urine samples were available for 3,997 pregnant women. Of these women, 92 reported having used cannabis during pregnancy (2.3%) and 71 had positive urine screens (1.8%). In total 35% of the 92 women with self-reported cannabis use also had a positive urine screen. Positive urines were relatively frequent in women reporting cannabis use before pregnancy only (7.6%) and in women with missing information (2.6%). Sensitivity and specificity of urinalysis compared to self-report were 0.46 and 0.98. Sensitivity and specificity of self-report compared to urinalysis were 0.36 and 0.99. Yule's Y amounted to 0.77, indicating substantial agreement between the measures. Conclusions: Our findings illustrate the difficulties in obtaining valid information on prenatal cannabis use. To improve the quality of cannabis use data, we suggest a 2-step approach starting with self-report. Copyright (C) 2010 S. Karger AG, Basel